The present invention relates to friction clutches in general, and more particularly to improvements in so-called clutch friction discs which are utilized in many types of clutches to transmit torque between driving and driven rotary components, e.g., in clutches for automotive vehicles to transmit torque from a crankshaft to the input element of a change-speed transmission. Still more particularly, the invention relates to improvements in clutch friction discs of the type wherein a rotary flange carries at least one blade which extends radially beyond the periphery of the flange and is assembled of two elastically deformable plates carrying friction linings of metallic, ceramic or other suitable material.
It is already known to provide the flange of a clutch friction disc with a plurality of radially outwardly extending blades each of which has two plates facing each other and carrying, at their outer sides, friction linings which are permanently affixed thereto by rivets. It is also known to provide each plate of each blade with an opening for the inner head of each rivet which connects the associated plate with the corresponding friction lining as well as with a rivet hole for the shank or neck of the rivel connecting the plate with its associated lining. Reference may be had to U.S. Pat. No. 1,652,007 granted Dec. 6, 1927 to Gamble. This patent discloses circumferentially complete friction rings at the outer sides of the plates and also the feature that one of the plates has a radially bowed portion enabling the clutch friction disc to yield when the clutch is engaged.
British Pat. No. 2,019,959 discloses a modified clutch friction disc with a central hub or flange for several blades each including two elastically deformable plates provided with friction linings which are secured thereto by rivets. The lateral portions of plates in each blade are coupled to each other by lugs whose bent-over end portions extend into complementary recesses of the neighboring plates. The median portions of the plates in each blade tend to move apart, i.e., the thickness of each blade increases when the clutch is disengaged. The inner heads of rivets which connect the linings to the respective plates penetrate into the openings of neighboring plates when the blades are flattened so that the rivets do not interfere with a reduction of the thickness of blades in engaged condition of the clutch.
German Utility Model No. 7,149,592 discloses a further clutch friction disc which also utilizes friction linings at the outer sides of plates forming part of blades at the periphery of a disc-shaped carrier or flange. The friction linings are installed in sockets which are mounted on the plates. Specially designed rivets are provided to secure the sockets to the respective plates as well as to limit the extent of movement of the plates in a blade away from each other.
In each friction disc, the plates which carry the friction linings are subjected to very pronounced thermal stresses which can result in localized overheating and can entail permanent deformation of corresponding portions of the plates. The extent of permanent deformation depends on the magnitude of internal stresses and can be sufficient to prevent satisfactory operation of the clutch, i.e., the friction disc is not likely to be properly separated from the neighboring component parts when the operator wishes to disengage the clutch. In such instances, the operator must exert a substantial force whenever he or she wishes to shift into a different gear, and the application of such force can lead to extensive damage to the clutch and/or to the transmission which receives torque from the engine in response to engagement of the clutch when the latter is used in an automotive vehicle.